Stability of solitary waves for generalized $abcd$-Boussinesq system: The Hamiltonian case

The $abcd$-Boussinesq system is a model of two equations that can describe the propagation of small-amplitude long waves in both directions in the water of finite depth. Considering the Hamiltonian regimes, where the parameters $b$ and $d$ in the system satisfy $b=d>0$, small solutions in the energy space are globally defined. Then, a variational approach is applied to establish the existence and nonlinear stability of the set of solitary-wave solutions for the generalized $abcb$-Boussinesq system. The main point of the analysis is to show that the traveling-wave solutions of the generalized $abcb$-Boussinesq system converge to nontrivial solitary-wave solutions of the generalized Korteweg-de Vries equation. Moreover, if $p$ is the exponent of the nonlinear terms for the generalized $abcb$-Boussinesq system, then the nonlinear stability of the set of solitary-waves is obtained for any $p$ with $0 < p < p_0$ where $p_0$ is strictly larger than $4$, while it has been known that the critical exponent for the stability of solitary waves of the generalized KdV equations is equal to $4$.